Emerging evidence indicates that hematopoietic stem cells (HSCs) are susceptible to oxidative stress. Reactive oxygen species (ROS), oxidative by-products generated during mitochondrial aerobic metabolism and energy production, can have a profound impact on HSC quiescence/cycling and self-renewal. The hypoxic microenvironment provided by stem cell niches limits the production of ROS in HSCs, preserving such an essential cell reservoir from oxidative damage. However, cell intrinsic mechanisms that limit metabolic activities and protect HSCs from oxidative stress are poorly defined. Furthermore, the mechanism by which cell metabolism orchestrates HSC lineage differentiation in concert with other regulatory networks has not yet been characterized. Lack of such knowledge impedes the understanding of the bioenergetic modulation of hematopoietic cell development and the pathogenesis of excessive oxidative stress-associated blood disorders, including hematopoietic cell malignancies. PTPMT1, an evolutionarily conserved PTEN-like phosphatase, is localized to the mitochondrial inner membrane where oxidative phosphorylation and ATP synthesis take place. The physiological function of this phosphatase is unknown. Our preliminary studies clearly suggest that PTPMT1 is essential for embryogenesis and adult hematopoietic homeostasis. It may play an important role in protecting HSCs from oxidative stress by limiting mitochondrial metabolism. Targeted disruption of PTPMT1 results in embryonic lethality at E.7.5, when embryonic cells have just started cellular respiration and oxidative stress. Haplo-insufficiency in PTPMT1 compromises lymphoid development in PTPMT1+/- mice. Deletion of PTPMT1 from bone marrow (BM) cells of conditional knockout (PTPMT1fl/fl/Mx-Cre+) mice impairs myeloid and lymphoid development. Intriguingly, ATP production in PTPMT1-ablated BM cells is enhanced. Notably, the role of PTPMT1 in hematopoietic cells seems to be selective, since there are no detectable morphological changes in PTPMT1-deleted hepatocytes in the liver from the same mutant mice. Nevertheless, the detailed cellular and molecular mechanisms by which PTPMT1 regulates hematopoietic cell development remain to be determined. Based on these preliminary findings we hypothesize that PTPMT1 facilitates the hematopoietic process by limiting energy metabolism and protecting stem cells from oxidative stress. We plan to test this hypothesis and accomplish the objective of this application by pursuing the following two specific aims. (i) Define the role of PTPMT1 in hematopoiesis. (ii) Determine the signaling mechanisms by which PTPMT1 facilitates hematopoietic cell development. The combination of the work proposed in the three Aims is collectively expected to yield new insights into the bioenergetic modulation of hematopoietic cell development. In addition, the information gathered will lead to a better understanding of the pathophysiology of oxidative stress-associated blood disorders. PUBLIC HEALTH RELEVANCE: The project proposed seeks to understand the role of the novel mitochondria-based phosphatase PTPMT1 in hematopoietic cell development. It is anticipated that the proposed studies will yield new insights into the bioenergetic modulation of hematopoietic stem cell function. Also, the information gathered will lead to a better understanding of the pathophysiology of oxidative stress-associated blood disorders.